Recently, an epitaxial silicon wafer has been used for high-performance devices such as MPU and a flash memory and high-performance power devices such as MOS FET and IGBT. As high integration of the devices proceeds, an improvement in quality of a semiconductor substrate and, especially, highly accurate flattening for manufacturing a minute pattern is becoming important.
In epitaxial growth on a silicon wafer, which requires a highly accurate flatness, evenness of a film thickness has been improved by a single-wafer treatment. Moreover, the evenness of the film thickness has been enhanced by controlling gas flow for the epitaxial growth using a partition and the like.
However, since a growth rate of the epitaxial layer is different depending on a crystal orientation, a film thickness of the epitaxial layer formed on a peripheral portion of the silicon wafer varies, so that it is difficult to uniformize the film thickness of the epitaxial layer on the peripheral portion of the silicon wafer. As a method for overcoming this difficulty, a technique of vertically moving a susceptor in a direction perpendicular to a mounting surface of the susceptor on a periodic basis depending on a periodic change of the crystal orientation on the peripheral portion of a semiconductor wafer, the change caused by a horizontal rotation of the susceptor, is disclosed (Patent Literature 1: JP-A-2014-67955).
Moreover, a susceptor including: a wafer mounting portion on which a wafer is mounted; a peripheral portion that surrounds a circumferential edge of the wafer mounting portion; and a vapor-phase growth controller that is provided on the peripheral portion and controls a speed of vapor-growth on a peripheral portion of a wafer to be mounted is disclosed (Patent Literature 2: International Publication No. WO2007/091638, Patent Literature 3: JP-A-2007-294942).
However, in Patent Literature 1, for instance, as for a silicon wafer having a crystal orientation in a (100) orientation, it is necessary to vertically move the susceptor every time the silicon wafer is rotated by 45 degrees. Accordingly, in association with the vertical movement of the susceptor, it is likely that a flow of material gas becomes turbulent near the susceptor or the silicon wafer slightly vibrates. Consequently, the film thickness of the epitaxial layer formed over an entire surface of the silicon wafer may become uneven.
Moreover, in Patent Literatures 2 and 3, it is necessary to prepare a susceptor having a complicated shape corresponding to the crystal orientation of the peripheral portion of the wafer, which entails an increase in a processing cost of the susceptor.